reproduction of apparent bug with .label() and not_() in SQLAlchemy

reproduction.ipynb

reproduction.py

# coding: utf-8

from sqlalchemy import create_engine
from sqlalchemy.schema import MetaData, Table, Index, Column
from sqlalchemy.sql import and_, or_, not_, select, text
from sqlalchemy.types import Text, Integer, Float, String

engine = create_engine('sqlite:///:memory:', echo=False)
metadata = MetaData()

user = Table('user', metadata,
    Column('user_id', Integer, primary_key=True),
    Column('user_name', String(16), nullable=False),
    Column('email_address', String(60)),
    Column('password', String(20), nullable=False)
)
user.create(engine)

with engine.connect() as conn:
    for name in ('jack', 'james', 'jenny'):
        email = '{name}@gmail.com'.format(name=name)
        ins = user.insert().values(user_name=name, email_address=email, password="bad_pass")
        result = conn.execute(ins)

with engine.connect() as conn:
    query = select([user])
    found = conn.execute(query).fetchall()
    print("Full results: {results}".format(results=found))

    query_with_disjunction = query.where(or_(user.c.user_name == "jack", user.c.user_name == "james"))
    print("SQL: {}".format(str(query_with_disjunction)))
    found = conn.execute(query_with_disjunction).fetchall()
    print("\nReturns: {results}.\nThat makes sense.\n".format(results=found))

    disjunction = or_(user.c.user_name == "jack", user.c.user_name == "james")
    query_with_negated_disjunction = query.where(not_(disjunction))
    print("SQL: {}".format(str(query_with_negated_disjunction)))
    found = conn.execute(query_with_negated_disjunction).fetchall()
    print("\nReturns: {results}\nThat makes sense.\n".format(results=found))

    disjunction_with_label = disjunction.label("labelled_disjunction")
    query_with_negated_disjunction_with_label = query.where(not_(disjunction_with_label))
    print(("Produces the SQL: {}\n\nNotice that the 'not' does "
           "NOT put parentheses around the disjunction".format(str(query_with_negated_disjunction_with_label))))
    found = conn.execute(query_with_negated_disjunction_with_label).fetchall()
    print(("\nReturns: {results}\n\nThat doesn't make sense for 2 reasons: "
           "1) we'd expect the same result as the unlabelled disjunction, i.e. just jenny and "
           "2) even if it's correct to apply the 'not' only to the first clause, "
           "the result should be james and jenny, not jack and jenny.\n".format(results=found)))

    literal_query = str(query_with_negated_disjunction_with_label.compile(
        compile_kwargs={"literal_binds": True}))
    print("If we pre-bind the variables and run directly, we get james and jenny:")
    res = conn.execute(literal_query).fetchall()
    print(str(res))